In order to produce small-sized, thin, and high-density electronic components, a multilayer board has been frequently used as a printed wiring board. By establishing a high-dielectric layer on the inner layer or surface layer of such multilayer printed wiring board, the package density is improved, and it becomes possible to produce smaller-sized, thinner, and higher-density electronic components.
In the conventional high-dielectric layer material, a ceramic sintered body obtained by molding ceramic particles and then sintering the resultant has been used. Thus, the size and form of the material has been restricted by a molding method. In addition, since a sintered body is very hard and fragile, it has been difficult to freely process it, and thus it has been extremely difficult to obtain any given shape or a complicated shape.
Under such circumstances, a composite dielectric body formed by dispersing inorganic dielectric particles used as inorganic fillers in a resin has drawn attention. Various proposals have been made for the use of, for example, a perovskite-type composite oxide as such inorganic filler with a high dielectric constant used in the aforementioned composite dielectric body. Also, the present applicant has previously proposed a perovskite-type composite oxide useful as an inorganic filler in Patent Document 1 below.
However, if a perovskite-type composite oxide is brought into contact with water, A-site materials contained in the structure thereof, such as Ba, Ca, Sr, and Mg, are particularly eluted. Thus, it has been pointed out that such elution of A-site metals may cause destruction such as the peeling of a resin interface or insulation deterioration due to ion migration.
For the purpose of improving resin dispersibility, a method of treating the surface of a barium titanate powder particle with a silane coupling agent has been proposed, for example (see Patent Documents 2-6, for example).
However, even if the particle surface of barium titanate is simply coated with a coupling agent, the effect of reducing elution of A-site metals such as Ba is low. Thus, it has been desired to develop an inorganic filler used in a composite dielectric body, in which the amounts of the eluted metals are reduced.    Patent Document 1: International Publication WO2005/093763, pamphlet    Patent Document 2: Japanese Patent Laid-Open No. 2003-49092    Patent Document 3: Japanese Patent Laid-Open No. 2004-253219    Patent Document 4: Japanese Patent Laid-Open No. 2005-2281    Patent Document 5: Japanese Patent Laid-Open No. 2005-8665    Patent Document 6: Japanese Patent Laid-Open No. 2005-15652